High-frequency signaling and communicating system



June 24 1924.

- E. H. SMYTHE ET AL HIGH FREQUENCY SIGNALING AND COMMUNICATING SYSTEM Filed my 5. 1920 7 Sheets-Sheet 1 w myemarsx [dW/h fi Smyf/ve. Sa/m/e/ B. W/'///am5 Jr.

E. H. SMYTHE ET AL HIGH FREQUENCY SIGNALING AND COMMUNICATING SYSTEM ts-Sheet 2 june 24 1924. i i-99,081 E. H. SMYTHE ET AL HIGH FREQUENCY smmuue AND commuurcx'rme SYSTEM Shea t a 7 Filed May 5, 1920 i F/y. a:

June 24 1924. I

E. H; SMYTHE ET AL HIGH FREQUENCY SIGNALING AND COMMUNICATING SYSTEM v Filed my 5, 1920 Sheets-Share? llzlili June 24 1924.

E. H. SMYTHE ET AL HIGH FREQUENCY smmmue'mn commumcmme SYSTEM 7 Sheets-Sheet 5 m/eflfors. faw/h hf Smy/fie. Samuel 5. MW/fams/r:

Filed May 5 1920 jm 24, 1924-. Maw

E. H. SMWHE ET M... HIGH FREQUENCY SIGNALING AND COMEiUNICA'I'ING SYSTEM .Filed May a, 1.920 .7 Sheets-Shget 6 June 24 1924.

HIGH FREQ Filed May 5 1920 'T Sheets-Sheet 7 F/gif stares EDWIN H. siviYTiiE,

BROOKLYN, NEW.

YORK, ASSIGNORS TO PATENT @FFICE.

0F EVANSTON, ILLINOIS, AND SAMUEL B. WILLIAMS, JR., OF

WESTERN ELECTRIC COMPANY, INCOR-h PORATED, OF-N'E W YORK. N. Y., A CO'RPOR-ATION'OF NEW YORK.

HIGH-IBREQUENCY SIGNALING AND COMMUNICATING SYSTEM.

Application filed May 5,

and SAMUEL B. \ViLLIAMs, J12, citizens of the United States, residing at Evanston, in the county of Cook and State of Illinois, and at Brooklyn, in the county of Kings and State of New York, respectively, have invented certain new and useful Improvements in HiglrFrequency Signaling and Communieating Systems, of which the following is a full, clear, concise, and exact description.

This invention relates to an-i mproved communicatiiig system, and more particularly to a communicating system of the type in which the control of switching mechanism and the establishment of communicating circuits'are automatically eii'ected through the medium of high frequency electrical oscillations, either transmitted through space in the form of electromagnetic waves or guided upon metallic conductors.

This invention isdirecte'd particularly toward increasing the number of stations thatmay be served in an automatic system of iiitercommunicatioii by a limited number of non-interfering carrier waves, or high frequency channels over which such waves are transmitted and received. Heretofore, in systems of this character, it has been customary to provide as many such high frequency communication channels as there were stations to be served, each channel being normally identified with a particular station as the means of access thereto. In the present system, only as many channels need be provided as the maximum number of simultaneously existing connections between stations, the number of channels therefor being only. a relatively small percentage of the number of high frequency stations for which inter-communication is to be provided. In accordance with this invention,'any one of a relativelvlarge number of high fre quency stations in the communicating system has access to and may use any one-that happens to-be idle of a relatively small number of high frequency carrier waves orcommunicating channels.

To this end, and to the end of realizing a number of other incidental advantages, it isthe object of the present invention to provide a system in which a plurality'of high frequency channels are made available for use. by a plurality of stations; in which any high nel frees the :by other calling stations in setting'up their.

1920. Serial No. 379,105.

frequency station may have the use of any one of the channels in establishing communiing, automatically tests the intercommunication channels that are provided and automatically selects one of these channels which is not at the time in use; in which the selected channel is appropriated by the calling station and is guarded against selection for use by any other station; in which means are provided for'preventing two or more calling stations from performing their channel testing and selecting operations simultaneously;

in which a channel is normally provided foe the common use of all of the stations, through which channel the stations that are not communicating with each other are normally in operative.relation; in which the use of this common channel by any calling station auto matically prevents its employment by any other station that calls While the channel is in use; in which means are provided for enabling the calling station, preferably through the medium of the common calling channel, to select the station with which 1 communication is desired, and to exclude the other idle stations that are not being called; in which means are provided for registering at the calling station the particular channel" that that station selects for use in establishing its connection; in which means are made operative upon the selection of the called station for tuning both the calling and the called station, under the control of the chan-' nel registeringapparatus, to the particular channel that has been selected for use; in which the timing of the calling and called stations to the selected communicating chancommon calling channel for use connections; in which each of the communicating channels may consist of a'pa r of high frequency carrier waves, while the common calling channel consists of a single high frequency wave, in which means are provided for automatically tuning each station for the transmission of a pair and thereception of the other wave of a particular one of the waves of the pair depending upon whether the station is the calling station or the called station; in which means are provided for enabling one station to control the tuning of another station for the transmission and reception of particular carrier waves or pairs of carrier waves; in which means are provided for preventing the release of the connection between two communicating stations from bringing those stations into operative relation with the common calling channel if the release occurs while the calling channel is in use; in which local lines associated with each high frequency station are prevented from obtaining access to the associated station while the station is in use either as a calling or as a called station, or when any other station of the system is using the common calling channel in setting up a connection; and in which means are provided for effecting the production of a busy signal and the release of a connection when the complete establishment of the connection is for any reason prevented. The foregoing are some of the principal objects that the system of the present invention attains. In addition the system embodies a number of other features incidental to those mentioned above, and incidental to its use as a part of a comprehensive system providing for automatic interconnection and intercommunication between the local stations associated with any of the high frequency stations of the system and the local stations associated with any other of the main stations. The manner in which the foregoing desirable objects and features are realized will be explained in the description that follows of the preferred embodiment of the system, and the structures through which the objects are attained will be more particularly defined in the appended claims.

The preferred embodiment of the invention is illustrated in the accompanying drawings, in which Figs. 1 to 6 inclusive show diagrammatically as much of the circuit organization as 1s necessary to enable the invention and the preferred manner of practicing it to be understood, and in which Fig. 7 1s a schematic representation of the general plan of the system.

In assembling Figs. 1 to 6 of the drawing to show the circuit organization, they are to arranged as indicated in Fig. 8.

Referring first to Fig. 7, this illustrates schematically a number of stations, R to each having associated with it a number of local stations, S to S* inclusive.

These stations are indicated in the present instance as radio stations, that is, stations betweenwhich interconnection and intercommunication is established. through the me dium of unguided high frequency waves transmitted through space. In the specification that follows the high frequency stations means for establishing connection between it and any of its local stations, and with radio or high frequency oscillation means for establishing communication between it and any of the other radio stations of the system. The radio communicating means of each of the radio stations are represented in the schematic drawing to comprise, in the present instance, a transmitting antenna TA and a separate receiving antenna RA. The medium of communication between the different high frequency stations is indicated to consist of high frequency oscillations either transmitted freely through space or guided over a metalllic conductor; and in the present instance these are represented by the broken line circles X to X inclusive. The broken line circle X is intended to represent the single carrier wave that is used as a common or calling carrier wave; andthe four pairs of broken line circles X to X inclusive are intended to represent four pairs of carrier waves any pair of which is available for noninterfering communication between any two of the stations of the system. The normal availability of the common or calling carrier wave X to all of the idle or non-busy stations R is represented by the broken lines which radiate from this circle to the receiving antennae RA of all of the non-busy stations. At the station Rthe common or calling carrier wave X is connected with the transmitting antenna TA to indicate that the station R, as a result of the call from its local station S has appropriated the calling wave and is using it to effect the selection of one of the other radio stations the receiving antennae RA of which are responsive to the calling wave. The receiving antennae RA of the calling station It is represented by the arrow-headed broken line to be in condition where it is testing for an idle one of the communicating carrier waves X to X inclusive. The first two of the four pairs of carrier waves are represented as being in use, the pair X being in use in establishing operative relation between local station S of radio station R and local station S of radio station R, and the second pair X being represented as being in use in establishing connection between local Station S of radio station E and local station S of radio station R". This condition of use, as will subsequently be explained, renders the two pairs of waves X and X unavailable for use by the calltempt to illustrate schematically the general ldea or plan of arrangement of the system, and does not pretend to show anything more than this. Furthermore, the invention contemplates such multiplication of the parts "or elements indicated in Fig. 7 as may prove desirable in practice. There may be a larger or smaller number of radio or high frequency'stations employed; and each station may have a larger or smaller number of associated local stations, or, if desired, the communicating apparatus supposed to be represented at one of the local stations may be located at and form part of the associated high frequency, station. itself. There may also be any desired number of communicating channels, such as the pairs of carrier waves, employed for taking care of the traffic for which provision is to be made-between the various high frequency stations of the system. For the sake of simplicity any station, such as S, is represented in Fig. 7 as having access to only one radio trunk, such as that terminating in the radio sta' tion R, but it will be described lateron in the more detailed account of the circuits and their operation how such a station S has a second-choice access to another radio trunk, such as that terminating in the radio station R, in case the trunk at station R happens to be busy at the time with another communication. Referring now to the preferred circuit organization as illustrated in Figs. 1 to 6 inclusive of the drawing, only as much of wiring of a single high frequency station or trunk and itsassociated local stations is shown as is necessary to enable the invention to be understood; it being possible for one skilled inthe art, by mere extension-and duplication of the wiring and apparatus illustrated, to organize a system of such capacity as may be desired. As illustrated in the circuit diagram, there is a high frequency station or trunkkRT with two associated local stations S and S. The high frequency station or trunk is provided with a high frequency terminal consisting in the present instance of the transmitting antenna TA and the receiving antenna RA; and also with certain conductive terminals, such as the spring jack 14, the passive terminals of aut'omaticl;,switches such as the selector switch indicated at 4:, and the active terminals of an automatic line switch indicated at 13. At the spring jack terminals 14 of the high frequency or radio trunk a connecting cord may be connected with the trunk by means of the plug 15, the connectmg cord being provided with the usual equipment including a calling dial 15'. When the radio trunk is being used as an outgoing trunk for calls ori mating in the associated local stations, as b, S, the local lines are connected with it through the medium of the line switch 2, and thence by way of the trunk 3 and the selector switch4. The line switch 2 may be of the type commonly known as the Keith line switch, and the selector switch 1 may be a selector switch of the Strowger type, the associated circuits for the control of these switches being of the sort ordinarily used; or any other of the well known arrangements used in' the telephone art for extending the connection of a telephone line to the central office apparatus may be substituted. When the radio trunk is used as an incoming trunk for the extension to one of the local lines of a call originating at some other high frequency station, the circuit of the trunk is extended through the medium of a line switch 13 and a connector switch 41, these switches being conveniently of the type and having the wiring arrangement of the switches referred to above.

It is customary in the art to make a distinction between automatic systems, the switches of which are controlled from a subscriberssubstation, and systems in which manual substations may be connected to an automatic system through the medium of an operators cord circuit, such as that shown having associated with it automatic switch-controlling means. The former type is called a full automatic system and the latter type, a semi-automatic system. The present invention is equally well adapted to be used in connection with either a full auto matic or a semi-automatic system and has been illustrated as having the necessary connections for both types. 1

The radio terminals of the trunk may consist of two antennae TA and RA, These antennae may be of any desired form, and should preferably be located at a sufficient distance apart to insure the selectivity of thereceiving antenna with respect to the energy. in the wave radiated by the transmitting antenna; or, if it is desired to locate the antennae'closer together power limiting devices may be used; or the lrresponsiveness I of the receiving antenna to the energy it receives from the transmitting antenna may be attained by any of the several methods that are available in'the art.

The medium that is employed in the present instance for effecting radio 'or high frequency communication between the transmitting antenna TA and the receiving antcnna,'such as RA, of the distant radio station, is a high frequency carrier wave, the oscillatory current for producing which is generated in the tuned-high frequency oscillator 171. The oscillator circuit may be of well known type, comprising a vacuum tube or thermionic oscillator with an oscillation circuit including inductively related induclances in the input and output circuits of the tube. The filament current for this oscillator and for the energization of the other oscillators and for the modulator and power amplifier of the transmitting antenna system is supplied by the filament current generator 148, and the plate current for these devices is supplied by the plate current generator 147. These generators are driven by the motor 146, the current supply for operating which is controlled by the relays 199, 200 and 220.

The carrier Wave produced by the high frequency oscillator 171 carries two intermediate frequencies, one of these. intermediate frequencies being generated by the oscillator 160 and the other being generated by the oscillator 168. Both of these are vacuuni tube oscillators and have oscillation circuits of the same type as the-carrier wave frequency oscillator 171 referred to above. The intermediate frequency oscillatory currents generated by the oscillator 160 are modulated by the voice currents transmitted from the telephonetransmitter of the associated local station; The voice currents from the associated local station pass over the talking conductors 97 and 98 of the trunk and through the four equal windings of the two-way repeating coil 119-into the balancing network 150. The junction points of the two serially included repeating.- coil windings in each side of the line circuit are connectedwith the input circuit of "a thermionic amplifier 151, and the output circuitof the amplifier is connectd by way of the inductive couplings 152 and 154 with the input circuit of the modulator 155.

The operation of the oscillating and modulating circuits herein disclosed, is

briefly as follows: The oscillator 160 and modulator 155 are supplied with plate current through the choke eo'il 161 which has sufficiently large inductance to prevent the passage therethrough of current fluctuations .of frequencies as high as those used in transmission of speech. The platecurrcnt supply circuit for the oscillator 160 contains also a choke coil 159 which transmits voice frequencies but has sufficient inductance to prevent the passage of current fiuctuations corresponding to the frequency of oscillator 160. Since the current supplied to the tubes 155- and 160 together in parallel is maintained constant Whereas the current through the tube 155 alone is controlled by the impressed voice current, the current through the oscillator 160 is made to vary in a complemental manner, and therefore the amplitude of the wave generated bythe oscillator 160 varies in accordance with voice currents received over the line eonductors. The frequency of oscillator 160 is controlled by the condenser 157 ,-while the condenser 156, which is too large to have an appreciable effect on the period of the ocsillator, serves to prevent short-cireuiting of the current supply.

The oscillators 160, 168 and 171 are all connected to and feed into the input circuit of the modulating tube 180. Condenser 178 aifords a high frequency by-pass for the radio frequency current from oscillator 171. The output coils from oscillators 160 and 168 are in series. However, the coupling of the oscillator circuits to-the common work circuit maybe made sufficiently loose to prevent reactionof one oscillator upon another and to prevent the constants of the Work circuit from affecting the period of the oscillator.

The action of the modulator 180 is somewhat different from that of 155 since all of the waves are impressed upon the grid circuit and the modulating act-ion depends upon the variation of the tube impedance to the passage of the radio frequency current under control of the currents impressed from oscillators 160'and 168. The result is that the radio frequency wave is modulated by each of the waves from the intermediate frequency oscillators each of which is, in turn, modulated or controlled by currents or waves of lower frequencies. The plate current circuit of the oscillator 160 and modulator 155 is controlled by contacts of a relay 215, so that the intermediate frequency generated by the oscillator 160 may be applied to or withdrawn from the carrier wave to produce signalirg impulses. The operation of the other intermediate frequency oscillator 168 iscontrolled at the contacts of the relay 216 and is ap lied to iii.)

the carrier wave for the purpose 0 guarding against the production by any other station of the particular frequency that 1s being transmitted by the oscillator 171. The intermediate frequency produced by the oscillator 168, therefore may be referred to as the guarding intermediate frequency and that produced by the oscillator 160 as the signaling and talking intermediate frequency.

The output circuit of the modulator 180 is inductively coupled with the tuned input circuit of a power amplifier 209 of the thermionic'type; and the output circuit of the amplifier is inductively coupled with the tuned transmitting antenna TA of the system. The tuning of the amplifier input circuit and of the transmitting antenna TA, as I '177, 275, 276, and 277, and these branches are respectively controlled by relays 181, 182, 183, 184, 282, 283 and 284 The tuning branches associated with'the power amplifier include adjustable condensers 195, 196,

'197, 198, 296, 297 and 298, and these branches are respectively controlled by relays 191, 192, 193,194, 292, 293 and 294. The tuning branches associated with the transmitting antenna include adjustable tuning inductances 211, 212, 213, 214, 312, 313, and

314, and the branches are respectively con-' trolled by relays 201, 202, 203, 204, 302, 303 and-304. For effecting the operation of the relays controlling the tuning branches there are seven energizing circuits, and each of these energizing circuits is connected with the windings of three of the controlling relays, one from each of the three tuning groups. The seven energizing paths or conductors are designated 272, 94, 95,96, 162, 163 and 164, the first of these conductors being connected with. the winding of the first relay in each of the three groups in the order in which these relays were mentioned, the second conductor with the winding ofthe secondrelay in each'group in the order mentioned, and so on.

. any one of the energizing paths is closed,

the corresponding relay in each ofthe three tuning groups is operated, and a corresponding tuning branch groups is closed.

The capaclties'and inductances included in each of the three in the seven branches of each of the three tuning groups are so adjusted that the closure of any one of the seven energizing. paths, with the consequent closure of the corre sponding tuning branch in each of the three groups, causes the production and application to the transmittingantenna of an oscillation having a frequency dlfiering from the frequency produced when any other one.

of the seven energizing paths is closed. In the present instances the frequency of the carrier wave oscillations thus applied to the transmitting antenna may conveniently have the following ratios; 100, 150, 225, 275, 350,

. 425 and 475, these frequencies being applied by the'energization of conductors 272, 94, 95, 96, 162. 163 and 164, respectively.

In the radio receiving part of the system, the receiving antenna RA of each station is inductively coupled with the tuned input circuit of the thermionic detector 230. 'The, output circuit of the detector includes serially the two frequency filtersv 235 and 236; and also has bridged across the filament and The seven tuning branches asso- Thus when plate circuit a condenser 237 for eliminating the unmodulated carrier frequency. The filter 235 has its constants s0 adjusted as to selectthe guarding intermediate frequency and to by-pass the signaling and talking intermediate frequency, and the filter 236' is adjusted to select the signaling and talking intermediate frequency and to by-pass the guarding intermediate frequency. The filter 236 is inductively coupled with the input circuit ol the detector 255, and the output circuitof the detector 255 is inductively coupled with the input circuit of the amplitier 259. The output circuit of the amplifier has two branches controlled in switching contacts of the relay 271. The norrlnally. closed branch is connected by way of the inductive coupling 263 with a cir cuit including two windings of the two-way repeating coil 149. The inductive relation of these two windings with the other windvoice current modulations that reach the called station through its receiving antenna are prevented from re-acting upon the radio transmitting system of that station and ,causing similar voice current modulations of the oscillatory currents passing to its transmitting antenna. The other branch of the amplifier output circuit, closed when relay 271 is operated, is connected ,through the inductive coupling 264 with the rectifier 269, and the circuit of the rectifier includes the winding of relay 268. The relay 268 is adapted to respond to the signaling and talking intermediate frequency of the carrier wave, and to act through the medium of conductor 35 to govern the operation of certain switching mechanism of the associated trunk.

The filter 235, which selects the guarding intermediate frequency of the carrier wave, is connected with the input circuit of the thermionic detector 238, and the output circuit of this detector is inductively coupled with the input circuit of the amplifier. 245, the output circuit of which in turn is inductively coupled with the circuit of the rectifier 251. The circuit of the rectifier includes the winding of relay 252, whih relay is thus adapted to respond t;/ the guarding intermediate frequency ofthe carrier wave and to act through themedium' of condurtor 100 to govern the operation of switching mechanism of the associated trunk.

The tuning of the receiving antenna system of the radio trunk-yis effected, in the particular embodiment of the invention illu trated, by means of seven branches inclurhng the adjustable condensers 231, 232, 233, 234, 332, 333 and 334, respectively. These branches are under the control of relays 221, 222, 223, 224, 322, 323 and 324, respectively. ing the condenser 231 and controlled by relay 221 is normally closed, and the other branches are normally open. The winding of relay 221 is included in a common portion of an energizing circuit having the six branches 42, 43, 44, 165, 166 and 167, and the windings of the other six tunin control relays are included one in each 0 these six branches. Therefore when any one of the six branches isclosed to operate the included relay and close the corresponding tuning branch, the relay 221 is operated to open the normally closed tuning branch that it controls.

The common portion of the energizing circuit that includes the winding of relay 221 also includes the winding of a relay 220 which, when it is operated, closes the energizing circuit of the motor 146 for driving the generators 147 and 148 to produce the plate and filament current, and also closes the circuit of relay 216 to energize the guarding intermediate frequency oscillator 168. Thus the transmittmg antenna system is energized to produce the carrier wave and apply the guarding intermediate frequency whenever any one of the six normally open tuning branches of the receiving antenna circuit is closed. It may also As has been stated, the first tuning branch of the receiving antenna system is normally closed, and the first tuning branch of the transmitting antenna system is closed by the completion of a circuit by way of conductor 1 272 upon the seizure'of the radio trunk by a calling local station, and at certain other times in the operation of the system, as will subsequently ,be described. The other six tuning branches of the receiving antenna system and the other six branches ofthe transmitting antenna system are selectively energized under the control of the tuning selector switch P. When the radio station is calling, one or another of the transmitting The tuning branch contain-v system tuning branches 94, 95 and 96, and one or another of the receiving system tuning branches 42, 43 and 44 are energized, depending upon whether the switch P is moved to its first, second or third position from normal. When the radio station is being called, one or another of the transmitting system tuning branches 162, 163 and 164, and one or another of the receiving system tuning branches 165, 166 and 167 are energized, depending upon the position to which the switch P has been moved. The arrangement is such that when the station is calling and the switch P has been moved to its first position from normal, the transmitting system is tuned, in the present instance, to a wave length of 150 meters and the receiving system is tuned to a wave length of 225 meters; while at the same time a corresponding movement of the tuning selector switch .P at the called station to its first position from normal causes the transmitting system of the called station to be tuned to a wave length of 225 meters and the receiving system at that station to be tuned to a wave length of 150 meters. Thus it will be seen that in this case the receiving system of the called station. is tuned to the carrier wave length, of 150 meters that the calling station is transmitting, and that the transmitting system of the called station is tuned to a carrier wave length of 225 meters that the receiving system of the calling station is tuned to receive. In like manner when the switches P at the calling and called stations occupy corresponding positions, the transmitting system of each station is tuned to send out a different carrier wave length to which the receiving system of the other station is tuned to respond. This arrangement may be tabulated as follows:

Additional sets of carrier wave lengths corresponding to additional positions of the switch P may, if desired, be provided by 0- adding other tuning branches to the transmitting and receiving antenna systems of the stations; and these branches may be ar-' ranged and controlled similarly to the arrangement and control of the branches that are illustrated. By bringing their switches P into corresponding positions, any calling station and the station that is being. called may use for communicating purposes any of,

these sets of wave lengths. The wave length a which is used only when a wave of a different frequency is employed, is commonly known as a channel or a high frequency communication channel. It will be seen that each terminal apparatus is capable oftransmitting or receiving through any one of a number of channels and that one such chan nel may be selected and appropriated for use by a pair of stations, to the exclusion of all other stations of the system and that the channels, by virtue of the different frequencies which they employ respectively, do not interfere with one another, but enable -inde pendent simultaneous communication between diflerent stations of the system.

As has been stated, the system is so arranged that each carrier wave may have applied to it two intermediate radio frequencies, one of which is modulated to carry the speech frequencies and also is applied and withdrawn to convey the signaling and switch controlling'impulses, and the other of which is modulated or controlled to guard against simultaneous use by some other station of the carrier wave to which it is ap plied. -These intermediate frequencies may have any desired value above the audio frequency and below the carrier wave frequency range. For example, the talking intermediate frequency may be twenty thousand and the guarding intermediate frequency may be fifty thousand. These two intermediate frequencies may be the same for all of the carrier waves employed, as the non-interference between simultaneously communicating pairs of radio stations is ensured by the non-interfering carrier wave lengths that are employed.

Each radio trunk has associated with it receiving register switch apparatus and transmitting register switch apparatus employed when the associ ted radio station is calling another radio t'ation, and addition al receiving register switch apparatus and transmitting register switch apparatus employed when the associated radio station is being "called by some other radio station.

The calling receiving register switch 'ap paratus consists of a station receiving register switch A. a carrier wave receiving register switch D, a tens receiving register with B, 31.4? un ts e e i gi er switch C. The calling transmitting register switch apparatus consists of a station transmitting register switch E, a carrier wave transmitting register switch G, a tens transmitting register switch K, and a units transmittingregister switch M. Each of these transmitting register switches has as sociated with it a change-over switch, F, H, L, and N. respectively, for interposing an interval between the operation of the associated switcheand the operation of the next switch in the series. The receiving register apparatus that comes into use when the radio station is called by another radio station comprises a station receivingre ister switch or station selecting switch R, a carrier wave receiving register switch V, a tens receiving register switch BR, and :1 units receiving register. switch OR. .The transmitting register apparatus that becomes active when the radio station is called by some other radio station comprises a tens transmitting register switch W and a units transmitting register switch Z. Each station also has a tuning switch 1 that operates when the station is the calling station to tune the transmitting antenna and receiving antenna systems to the pair of carrier waves registered by the carrier wave receiving register switch D; and which 0})- erates whenithe station is the called-station to tune the transmitting and receiving antenna systems to the pair; of carrier waves indicated by the carrier wave receiving register switch V. There is also at each station a switch Y that operates to apply a return signal for a predetermined length of time to the transmitting antenna 4 system at the called station and then w1thare well known in the art and need not be particularly described.

Associated with the radio trunk in the form in which it is herein disclosed are also a number of plunger relays; as 73, 79, 46,

'52, 62, 101, 118, 127 and 136, which are employedv to introduce relatively large time intervals into the operation of certain parts ofthe organization. The plungers of these relays are retarded in theirinward movement and are permitted to move freely on their return-movement. They may be of the type disclosed in V the; appllcat'l'on' of Samuel B. Williams, Jr, and Walte Albert, Serial Number 146,671, filed February 5, 1917.

Briefly stated, the operation of the particular embodiment of the system here'disclosed is as follows: When a subscriber wishes connection with another subscriber whose station must be reached through a radio trunk, the taking of his telephone receiver from its hook causes his line switch to extend the circuit of his line to a selector switehfand this switch is operated in response to the first transmitted group of impulses to bring its switch wipers into engagement with the terminals of the first of the radio trunks that may be provided for serving the local stations of this exchange group. If the radio trunk is in usecither in establishing an outgoing connection to some other radio station or in establishing an incoming connection from such a station, or if some other radio station is using the common or calling carrier wave to extend a call, there is a busy test potential on the terminals of the trunk, and the selector switch is prevented from making connection with the trunk and proceeds to the next trunk. 'If the trunk is not in use, the selector switch establishes connection with the trunk terminals, and the trunk is energized to send out the common or calling carrier wave with its guarding intermediate frequency. The second movement of the dial at the subscribers station sends a group of impulses for determining the distant radio station to which the connection is to be ex-' tended, andthe third and fourth movements of the dial produce impulses in accordance with the tens and units digits of the local line with which connection is desired at the called radio station. The groups of impulses produced by the second, third and fourth movements of the calling station dial are recorded respectively upon a station receiving register switch, a tens receiving register switch and a units receiving register switch.

Immediately upon the seizure of the radio trunk by the calling subscribers line, the calling radio station proceeds automatically to tune its receiving antenna system to one after the other of the pairs of individual or communicating carrier wave frequencies. If the pair of individual carrier waves tested 1s,in use, the response of the receiving antenna system of thecalling station causes it to be tuned to the next pair of individual carrier waves. If all of the pairs of individual carrier waves happen to be in use, a busy tone is transmitted to the calling subscribers station, and the connection is released when the calling subscriber hangs up. If one of the pairs of individual carrier waves is found not in use, the identity of the available pair of carrier waves is recorded u on a carrier wave receiving register switc the receiving antenna system of 'scribers telephone the calling radiostation is again tuned to the common or calling carrier wave frequency, and the transmitting antenna system of the calling radio station proceeds to send out impulses upon the signaling iutermediate frequency of the common or calling carrier wave corresponding in number to the impulses recorded upon the station receiving register switch.

At each radio station of the system that is not in use, the impulses of this group cause the corresponding advance of a station selecting switch. Each of these station selecting switches is arranged to bring its associated station switching apparatus into operative relation with its receiving antenna system only when the switch is ad-/ vanced to a particular point by the impulses received from the calling, radio station; and this point differs with the station selecting switches of the different radio stations, so that for a certain number of impulses transmitted from the calling station over the common carrier wave one only of the other radio stations is placed in operative relation with the calling station at the end of the station selecting impulses All of the other stations are left inoperative-and unresponsive to the succeeding groups of impulses, and are returned to operative condition only when the common carrier wave is withdrawn quency from the common carrier wave, but

continues to apply the wave with its guarding intermediate frequency, and also causes.

the calling station receiving antenna system during this interval to be responsive. to the signaling intermediate frequency of the common carrier wave. At the same time, and during the same interval, the called radio station ifit has been selected applies the common carrier wave with its signaling intermediate frequency. As a result, if the called radio station is available, and has responded to the signaling impulses sent from the calling station, it sends out the, common or calling carrier wave with its signaling intermediate frequency as a return signal; and the receiving antenna system of the calling radio station responds to this return signal and releases its apparatus to proceed with the next stage of the operation. If the calling station does not receive this return signal within a predetermined time interval, it applies a busy tone to the calling subseribers line, and the connection is released upon the hanging up of the calling subreceiver. When the called radio station hassent its return signal, it withdraws the common carrier wave with its signaling intermediate frequency and remainsresponsive to the common carrier wave with its uarding intermediate frequency that the calling radio station has continuously sent out, so that if for any reason the calling radio station fails to receive the return signal and consequently releases the connection, the withdrawal of the common carrier wave with its guardin inter mediate frequency causes the called radio station also to release its apparatus and return it to normal.

When the called radio station has been selected and has sentout its return signal, and the calling radio station has responded to this signal, the response causes the calling radio station to send out a series of groups of impulses corresponding to the groups of impulses'recorded upon the .carrier wave receiving registerswitch, the tens receivmg register sw1tch.and the units receiving re 'ster switch at the calling radio station. ese groups of impulses, which are sent out upon the signaling intermediate frequency of the common carrier wave, are respectively recorded upon a carrier wave receiving register switch, a tens receiving register switch and a units receiving register switch at the called radio station. When the sendin of the last group of impulses at the ca 'ng radio station and, its receipt and registration at the called radio station are com leted, tuning control switches at the calling and called radio stations become simultaneously operative for bringing the transmitting and'rcceiving antennee systems at these stations into tune with the pair of communicating carrier ,wave frequencies that.has been selected for use, the antennae. systems at both stations at the same time discontinuing and being made unresponsive to the calling carrier wave frequency. The tuningcontrol switch at each station selects the pair of carrier. waves that has been recorded upon the carrier wave receivi g register switch of the associated station, he transmitting'antenna system of the calling station and the receiving antenna system of the called station'being tuned to one wave frequency of the pair, and the transmitting antenna system of the called station and the receiving antenna system of the calling station being tuned to the other frequenc of the pair.

Imme iately upon being tuned to the selected air of communicating carrier waves the ca 'ng radio station applies to its transmitting antenna system its wave of the pair to the calling subscribers line and the connection released when the callin subscriber hangs up the release of the cal ing station apparatus also bringing about the release of the called station apparatus through the withdrawal of the guarding intermediate frequency that is applied to the individual or communicating carrier wave of the calling station from the moment that the tuningcontrol switch at the calling radio-station operates. If, however, the test made by the calling radio station indicates the presence of the called station carrierwave with its guarding intermediate frequency, the cal ling station actsto close the talking circuit of the radio trunk. v

In the meanwhile the radio trunk at the I called station has been operating from the moment the receipt of the last group of selecting impulses was completed, to extend the circuit of the called station radio trunk to the local line that is being called. This is'accomplished by a tens transmitting register switch and a units transmitting register switch that send to'a local trunk, to which the radio trunk has become extended, impulses to cause the selective operation of a connecting switch associated with thelocai trunk. The tens and units transmitting register switches send impulses in accordance with the impulses recordedupon the associated tens and units receiving register switches of the called radio station, thus op erating the automatic connecting switch of the local trunk to extend the trunk to the called subscribers line, and closing the talking circuit of the radio trunk when the line has been selected to complete the conversational connection.

At the end of the conversation, the hanging up of the telephone receiver at the calling subscribers station releases the apparatus of I the calling radio trunk and restores it to normal; and the restoration to normal of the calling radio trunk withdraws the calling station communicating carrier wave of the pair with its two intermediate frequencies. This causes the release and return to normal of the apparatus of the called station radio trunk. Inreturning to normal, the receiving antenna systems of bot-h radio stations are again made responsive to the common or calling carrier wave with itsintermediate frequencies: excepting that if the release of the connection occurs at a time when the common carrier wave is in use by some other radio station, the apparatus of the two re- .leased stations do not become responsive to the .common carrier wave until after the radio station that is calling has completed its calling operation and withdrawn that wave.

In detail the operation of the system 1s as follows :Let it be assumed that the subscriber at station S desires to get into communication with another subscriber whose station is at a remote exchange with which connection is had by means of radio. The subscriber at station S takes his telephone receiver from its hook, and the resultant operation of the associated line switch 2 connects the circuit of the calling line with an idle trunk 3 extending to a selector switch 4. The means for effecting this operation is well known in the art, and need not be described in detail. The calling subscriber at station S then proceeds to operate his calling dial 1 to produce the groups of impulses that control the operation of the automatic selecting switches. The first group of impulses may be employed, in a well known way, to cause the operation of the selector switch 4 to bring its wipers into engagement with the terminals of the branch RT of an idle radio trunk RT.

When the calling line is thus extended to the radio trunk, a circuit is closed through the subscribers station apparatus and over the conductors of the calling line that brings about the energizaticn of the line relay 6. Relay 6 in operating closes a circuit that extends from battery through the winding of the slow-release relay 7, front contact and armature of relay 6, and right-hand back contact and armature of relay 8 to ground. Relay 7 in operating opens at its upper back contact the circuit subsequently used to restore the register switches, closes at its upper front contact a circuit for rendering effective the controlling and sending apparatus of the radio trunk, closes at its middle front contact a test circuit for making the radio trunk test busy, and prepares at its lower front contact a circuit for transmitting impulses under the control of line relay 6. The 'test circuit for making the radio trunk test busy extends from battery through the winding of relay 5, inner left-hand back contact and armature of relay 9, outer lefthand back contact and armature of relay 8, and middle front contact and armature of relay 7 to ground. Relay 5 in operating, at its outer left-hand front contact and armature, connects battery to the sleeve of spring jack terminal 14 associated with branch RT of the radio trunk; and at its inner left-hand front contact and armature connects ground to the test contact of line switch terminal 13 ofthe branch RT of the radio trunk. At the same time, relay 5 in operating opens at its outer left-hand back contact the circuit over which. relay 9 is adapted to be energized by the insertion of plug 15 into spring jack terminal 14 of theradlo trunk; and at its inner left-hand back contact it opens the circuit over which the relay 11 of the line switch 13 is adapted to be held operated when the radio trunk is seized by a' call from a distant radio station; Relay 5 in operating also opens at its right-hand back contact and armature the branch including conductors 17 and 18 and retardation coil 16 over which impulses for the operation of line switch 13 and its associated connector switch 41 are transmitted by the operation of relay 107 when a call is received from a distant radio station.

It has been assumed that the first group ofimpulses determined by the operation of the dial 1 at the calling subscribers station S has resulted in the seizure of the radio trunk RT. Upon the first of the interruptions of the line circuit in connection with the second group of impulses that is now transmitted by the operation of the dial, line relay 6 releases its armature; and as relay 7 is slow in releasing and'holds its armatures closed during the short interruptions that constitute the impulses, a circuit is completed that extends from battery through the winding of the stepping magnet a of register switch A, winding of associated slow release relay 36, normal contact and wiper A of register switch A, conductor 28, lower armature and front contact of relay 7, back contact and armature of line relay 6, and right-hand back contact and armature of relay 8 to ground. The impulse thus produced causes. the register switch A to take one step, thus breaking the initial energizing circuit by way of wiper A- but an alternate energizing path has been closed at the left-hand front contact and armature of relay 36, and as the relay 36 is slow in releasing, this energizing path through the winding of relay 36 and the winding of the magnet of switch A is maintained during the impulses of the group that are now being transmitted. The register switch A therefore takes one step for each of the impulses of the group, and at the end of the group line relay 6 remains energized, thus holding open the pulsing circuit by way of the windlng of relay 36 and the winding of the associated stepping magnet a of registerswitch A, thus permitting relay 36 to release. The advance of theswitch ,wipers of the register switch A has caused the wiper A to close a path extending by way of outer right-hand back contact and armature of relay 36, conductor 27, and upper front contact and armature of relay 7 to grou d, thus identifying the stationary contact of switch wiper A that corresponds in position in its row to the number of impulses in the group that has just been transmitted.

The release of relay 36 at the end of the first group of impulses extends the pulsing conductor 28 by way of register switch wiper A to the next register switch B of the series, and the group of impulses determined by the next operation of the dial at calling station S causes the advance of the register switch B in the same manner as has been described in connection with ment the seizure of the radio trunk-by the calling line 15 completed, it closes acircuit, that extends from .battery through the winding of relay 31, lower back contact and the operation of the first'register switch A.

The first impulse of this groupoperates and locks up the relay 38 associated with register switch B; and when switch B has advanced its wiper B to' a point corresponding to the number of impulses in this particular roup, the cessation of the impulses causes tic release of relay 38, and the e. tension of the pulsing conductor 28 to the next register switch The succeeding group of impulses determined by the operation of the dial 1 at the calling subscribers station S causes the advance of the wipers associated with register switch C in the same manner as described in connection with the operation of register switches A and B, the wipers being advanced to an extent corresponding to the number of impulses in this group, and-the relay 39 holding its armatures attracted during the receipt of the impulses, and releasing'them at the end of the group. The register switches A, B and C are thus set in accordance with the numbers consecutively pulled upon the dial 1 at calling subscribers station S. As. the system is organized in this particular embodiment, the setting of the register switch A is in accordance with the particular radio station that has associated with it the line of the subscriber who is being called, and the register switches B and C are set respectively in'accordance with the tens and units digits of the called subscribers line. If a greater number of subscribers lines are .included in the group of lines associated with the radio station, then as many additional register switches such as B and C as are necessary may be included with their associated equipment to provide for the registration of the directory number of the called subscribers line. V

. Concurrently with the registration upon the register switches A, B and C of the num- :bers pulled upon the calling subscribers Station dial, apparatus associated with the radio trunk has been operating to approrlate the common or calling carrier wave, 1f that wave is not at the time in use by some. other radio station, and to select and approprlate apairof individual or communicating carrier waves for the subsequent use of the calling subscriber in establishing com municating relation with the called subscrlber. When relay 7 operates at the m0- armature of relay 40, conductor 26, lower back contact and armature of relay 10, and upper frontqcontact and armature of. relay 7 to ound. Relay 3 1 in operating closes a circu t that extends from battery through the winding of relay '33, inner -right-hand armature and back contact of relay 116, it being assumed that the common carrier wave is not in use by some other radio station, and right-hand front contact and armature of relay 31 to ground. If the common carrier wave happens to be in use,-relay 116 wil be in its operated condition, as will subsequently be explained, and consequently the energization of relay 31 will not act to bring about the operation of relay 33 until the common carrier wave is released by the other radio station that isusing it. Butassuming' that the common carrier wave. is not in use, the relay 33 is operated and acts to start the train of operationsthat results in a pair of individual carrier waves being selected, and radio impulses sent out in accordance with thesetting of the register switches to select the desired radio station and the desired subscribers line at that station.

When the relay 33 operates, in the movement of its outer armature it shifts the con ductors extending from the contacts of the signaling intermediate frequency relay 268 and. guarding intermediate frequency relay 252 v (Fig. 6), from their normal control over the radio signal receiving apparatus of the trunk, and gives them control over the radio signal' transmitting apparatus of the trunk. In the movement of its middle armature the relay 33 closes a circuit that extends from battery through the right-hand arn1a-- ture and back contact of relay 199 (Fig. 5),

winding of relay. 200, then in parallel.-

through the windings of relays 201, 191 and 181 of the radio transmitting system, conductor 272, left-hand armature andback contact of relay 114, conductor 34, normal contact and wiper P of switch P and middle front contact and armature of relay 33 to ground. The closing of this circuit op'erates the relays 200, 201, 191 and 181. Relay 200 in operating starts the operation ofthe motor 146, and the associated generators 147 and 148 are driven to generate, respectively, the plate current and the filament current for the energization of the radio transmitting system. Relay 200 in operating also closes at its lower front contact and armature'acircuit by way of the outer right-hand llO back contact and armature of, relay 114for v energizing relay 216, and that relay in operating connects the source of plate current 147 with the guarding intermediate frequencyoscillator 168, to cause the oscillator toap'ply this intermediate frequency to the carrierwave. At thesame-timev the high energization of the oscillator 171 upon the startlng into operation of the plate current generator 147 and filament current generator 148. The operation of the relays 181,

frequency carrier wave is applied by the I 191 and 201 acts to tunethe input circuit of p the modulator 180, the input circuit of the power amplifier 209, and transmitting the branches by way of capacities 232, 233,

23%, 332, 333 and 334: and their associated controlling relay contacts being open. On account of the tuning due to the closure of the path by way of capacity 231 the common carrier wave energizes the radio receiving system at each such station, and the superposed guarding intermediate frequency is separated out by the frequency tilter 235 and causes the energization of the associated detector 238, amplifier 245, and rectifier 251,

the rectified current flowing through and energizing the guarding relay 252. The guarding relay at each of the non-busy stations in operating closes a. circuit that extends from battery through the winding of relay 115, (Fig. 2), left-hand back contact and armature of relay 33, conductor 100, and front contact and armature of relay 252 to ground. At the radio stations that are in use, as calling stations, this circuit is kept open by the energization of relay 33 that results from the seizure of the radio trunk by the calling subscriber. as previously described; and at all radio stations that are using individual carrier waves for conversation. the receiving antenna system is tuned not to respond to the common or calling carrier wave.

Therefore, upon the seizure of the associated radio trunk by calling subscriber's station and the consequentapplication of the common carrier wave with its guarding frequency, the relays 115 at all of the radio stations that are not' in use are immediately energized. \Vhen relay 115 operates it closes at its upper front contact and armature a circuit by way of the inner upper armature andback contact of relay 124: for operating relay 116; and relay 116 in operating locks up by way of its inner left-hand front contact and armature and the normally closed inner contact 120 of timer 118 to ground. Relay 116 in. operating also breaks, at its inner right-hand back contact and armature, the path over which relay 31 brings about the operation of relay 33 when relay 31 is energized by the seizure of the associated radio trunk by a local calling line. Therefore the immediate effect of the transmission of the common carrier wave. with its guardfrom ground by way of right-hand armature and back contact of relay 31, right-hand a'rn'iature and back contact of relay 116,

winding of relay 21 and conductor 93, the.

subsequent. closureof which acts to restore the associated receiving register and other switches that may in the meanwhile have been stepped from their normal positions.

Rela 116 also closes a circuit that extends .from battery through the winding of relay 271 (Fig. 6), inner right-hand armature and back contact of relay 11 1, conductor 99, lower back contact and armature of relay 87, outer right-hand front contact and armature of relay 116, and right-hand back contact and armature of relay 31 to ground. Relay 271 in operating as a result of the closure of this circuit disconnects from the coil 263 the signaling and talking intermediate frequency branch of the receiving antenna system, and connects it by way of coil 26 1 and rectifier 269 with the signal receiving relay 268. Thus each nonbusy station is placed in a receptive condition with respect to the selecting impulses that are about to be transmitted from the calling radio station.

lVhen relay 115 at each of the non-busy radio stations operates, it closes a circuit that extends from battery through the winding of relay 105, inner lower front contact and armature of relay 115, outer upper armature and back Contact of relay 124;, and righthand back contact and armature of relay 31 to ground. Relay 105 in operating locks up by way of its inner left-handfront contact and armature and inner rest-ing contact 1 04 of timer 101 to ground. Relay 105 in operating also closes a circuit that extends from battery through the winding of relay 5 (Fig. 1), inner left-hand armature and back contact of relay9, outer back contact and "left-hand armature of relay 8, conductor 106, back contact and armature of relay 1.70, conductor 122, right-hand armature and back contact of relay 31, and inner right-hand front contact and armature of relay 105 to ground. Relay 5 in operating applies a busy test potential to the test terminals of line switch 13 and spring jack 14; and the grounding of the energizing circuit of relay 5 also produces a busy test condition on the selector switch terminal 1 of the trunk. Thus the non-busy radio trunk is safeguarded against seizure at any of its local terminals while any other radio station is calling.

Returning now to the operations that are taking place at the calling radio station, the relay 33 in attracting its armatures not only applies the common carrier Wave and its superposed guarding intermediate frequency as described, but also closes a circuit that extends from battery through the winding of relay 37, switch wiper P and normal contact, switch wiper D- and normal contact, and middle front contact and armature of relay-33 to ground. Relay 37 in operating locks up by way of its inner right-hand front contact and armature, and inner contact 53 of timer 52 to ground. Relay 37 inoperating also closes a circuit that extends from battery through the winding of the stepping magnet d of switch D, the armature and back contact of this magnet, switch arm D and its normal contact, and inner left-hand front contact and armature of relay 37 to ground.

The effect of the closure of this circuit is to cause switch D to take one step, the advance of the switch wipers to their second position breaking the energizing circuit of the stepping magnet atswitc-h arm D.

The above described movement of the switch arms of switch D closes a circuit that extends from battery through the winding of relay 271 (Fig. 6), inner right-hand inmature and back contact of relay 114, conductor 99, inner lower armature and back contact; of relay 60, off-normal contacts and switch arm D- of switch D, normal contact and switch arm P", inner right-hand front contact and armature of relay 37, and inner contact 53 of timer 52 to ground. The effect of the closure of this circuit is to operate relay 271; and this relay in operating disconnects-the signalling'and talking intermediate frequency branch of the receiving antenna circuit from its normal connection with the talking circuit of the trunk, and connects it instead through the inductive coupling 264 to the rectifier 269 which modifies the re contact from normal and associated ceived current for the operation of relay 268. The movement of switch D to its first po-- sition from normal also closes a circuit that extends from battery through the winding of relay 220 (Fig. 5), winding of relay 221, winding of relay 222, conductor 42, fi t swit dh arm D of switch D, and inner left-hand front contact and armature of relay 37 to ground. As a result relays 220, 221 and 222 are all operated. Relay 220 in operating, closes branches to ground of the ener gizing circuits of the motor '146 and of re-; lay 216, in parallel with the branches that are already closed in cjintacts of the relay 200. Relay 221 in operating opens the condenser branch 231 that normally tunes the receiving antenna circuit to the common carrier wave;'and relay 222 in operating closes the condenser branch 232 that tunes the receiving antenna system to one of the carrier wave frequencies of the first individual pair. Therefore, asa result of the first step taken by switch D on the operation of relay 37, the signalling intermediate" frequency relay 268 (Fig. 6) is brought into operative relation with the receiving anten na system, and the receiving antenna system is tuned to the frequency of one of the waves of the first individual carrier wave pair. As will subsequently be described, when any of the pairs of individual carrier wave frequencies is in use between two of the radio stations, each of the two stations transmits a different one of the high frequency waves of the pair with the signaling or talking intermediate frequency constantly impressed upon it. Therefore, if the first pair of individual carrier waves is in use, when the receiving antenna system of the calling radio'station is tuned to either one of the frequencies of this pair, the superposed signaling or talking intermediate frequency is detected, amplified, and rectified, and causes the operation ofrelay 268. When relay 268 operates it closes a circuit that extends from battery through the winding of the stepping magnet d of switch D, armature and back contact of this magnet, outer resting contact 45 of timer 46, outer righthand front contact and armature of relay 37, outer right-hand front contact and armature of relay 33, conductor 35, and front contact and armature of relay 268 to ground. The stepping magnet d attracts its armature, and in doing so opens the short circuit that normally exists by way of the back contact of the stepping magnet armature around the high resistance winding of slowrelease relay. 47. Relay 47 then operates and closes a circuit for the operation of relay 48 by way of front contact and armature of relay 47 and inner resting contact 49 of.

timer 46 to ground. Relay 48 in operating locks up by way of its inner left-hand front contact and armature and timer contact 49 to ground; and also, at its outer left-hand front contact and armature, closes a circuit for the energization of the timer 46. Timer 46 consequently starts the slow inward move- 0 cuit that had previously existed for the operation of tuning relay 222 (Fig. 6), and

closes, by way of conductor 43, an energizing circuit for the operation of tuning rela'y 223. As the energizing path for the operation of relays 220 and 221 is common to the branches through the various tuning relays,

the relays 220 and 221 remain energized when the branch through one of the tuning m) 

